The present invention relates to an analog voltage memory device capable of holding the difference between or sum of two analog input voltages.
There have been devised and demonstrated various types of analog voltage memory devices capable of obtaining the correct difference between or the sum of two analog input voltages and holding the result for a long time, but so far they have been unsatisfactory in practice because their circuits are complex and operations are not reliable.
In view of the above, one of the objects of the present invention is to provide an analog voltage memory device which may derive the correct difference or the sum of two analog input voltages at an arbitary time and hold the result precisely for a considerably long time and is very simple in construction, inexpensive to manufacture and highly reliable in operation.
Briefly stated, to the above and other ends the present invention provides an analog voltage memory device comprising a differential amplifier for deriving the difference between two analog inputs, an operational amplifier having a noninverting input end connected to the output end of said differential amplifier, analog switching means having one end connected to the output circuit of said operational amplifier, a MOS type field-effect transistor having the gate connected to the other end of said analog switching means and the source connected to a noninverting input end of said operational amplifier, a nonpolarized capacitor interconnected between the gate of said MOS field-effect transistor and a negative power source or ground, and an output resistor interconnected between the source of said MOS field-effect transistor and said negative power source or ground, whereby the output of the differential amplifier may be derived as a source follower voltage of the field-effect transistor and held for a considerably long time.
According to the present invention, the sum of or difference between two analog inputs may be derived by a circuit which is very simple in construction and is held precisely for a considerably long time. Therefore an analog voltage memory device in accord with the present invention may be advantageously used in conjunction with a measurement instrument for sampling the sum of or difference between two analog inputs thereto and holding the result. In addition, the present invention finds wide applications in medical appliances.
The above and other objects, features and advantages of the present invention will become more apparent from the description of three preferred embodiments thereof taken in conjunction with the accompanying drawings.